1. Field of the Invention
The present invention relates to a speaker device capable of reproducing sound in high quality tones.
2. Description of the Related Art
In a conventional speaker device, a vibration plate is electrically driven in a speaker unit. A vibration of the vibration plate is converted to an acoustic output. In the speaker unit, the acoustic output is generated by the vibration plate that is formed into various profiles such as a cone, flat plate, dome or the like. In order to generate a driving force to drive the vibration plate, an electrodynamic type driving section is used. In the electrodynamic type driving section, a magnetic circuit, the magnetic flux source of which is a permanent magnet, is used. In the magnetic circuit, magnetic flux is concentrated in a space referred to as a magnetic gap, so that an electromagnetic driving force can be generated in a voice coil in the magnetic gap. In the speaker unit, a frame holds the magnetic circuit, and the vibration plate is supported so that the voice coil can be displaced in the driving direction. Usually, a surface of front side of the vibration plate on which the magnetic circuit is not arranged serves as an acoustic emission face. A displacement of the surface of the vibration plate generates a compressional change in the air, so that an acoustic output is emitted into the space. The displacement of the vibration plate generates an acoustic output on the back side as well, the compressional phase of which is inverse to that on the surface side. When the acoustic output on the acoustic emission face side and the acoustic output on the back side are mixed with each other, since the phases are inverse to each other, the acoustic output of the vibration plate is lowered. This influence given by the acoustic output on the back side is remarkable in the sound region of low frequency (bass).
In many cases, in order to effectively obtain an acoustic output from the acoustic emission face of the vibration plate of the speaker unit, the speaker unit is accommodated in an enclosure such as a cabinet or a speaker box so that an acoustic output from the back side can not come to the side of the acoustic emission face. Only the acoustic emission face of the vibration plate is exposed to a surface of the enclosure.
In the speaker unit, a reaction of the motion of the vibration plate to generate sound tends to be transmitted to the frame side and causes vibration in the frame and the magnetic circuit. Since energy to drive the vibration plate leaks to a support system such as the frame, an intensity of energy, which is transmitted from the vibration plate to the air to become an acoustic output, is reduced, and the energy transmitting efficiency is lowered. By the energy that leaks to the support system, there is a possibility that each portion composing the speaker unit and the enclosure vibrate at their natural vibration frequencies, while being induced by the drive of the vibration plate. The thus generated vibration continues even after the driving of the vibration plate is stopped. The thus caused sound remains and is mixed with the acoustic output to be originally reproduced. This deteriorates the transient characteristic of the reproduced sound and the reproduced sound quality is lowered because the feeling of speed of the reproduced sound is hurt. In order to enhance the feeling of speed of the reproduced sound, it is advantageous to use a speaker of a small diameter, the vibration plate diameter of which is small, because the weight of the vibration system is decreased and the transient characteristic is enhanced. However, only when the diameter is decreased, mass of the air loaded on the surface of the vibration plate is decreased. This is disadvantageous in that the minimum resonance frequency is increased. In order to enhance the reproduced sound quality of the speaker device, it is necessary to suppress the occurrence of unnecessary vibration caused in each portion. In general, when mass of the frame of the speaker unit and the magnetic circuit is increased and mass of the enclosure is also increased, unnecessary vibration of each portion is seldom caused.
JP-UM-A-6-66194 discloses the following prior art. In order to reduce the occurrence of vibration and resonance while decreasing the weight of the speaker system, a plurality of speaker units are arranged on the horizontal face so that the axes of the speaker units can be dynamically balanced with respect to the direction of the motion of the vibration system. Further, the plurality of speaker units are arranged so that the axes have the same angle of elevation with respect to the horizontal face on the vertical face. The support systems of the speaker units are bound by a binding member, the rigidity in the axial direction of which is high. In this prior art, in the case where the number of speaker units is two in which a magnetic circuit is provided on the back of a vibration plate, although the magnetic circuits are opposed to each other on the horizontal face, since the speaker units are tilted by a predetermined angle of elevation with respect to the horizontal face, the axes of the two speaker units are not located on the same straight line but the axes of the two speaker units are tilted to each other and sound are reproduced. Therefore, the binding member is also joined to an inner wall face of the cabinet on the extension of the axis of each speaker unit.
Japanese Utility Model Registration No. 3008172 discloses the following prior art of a wall mounting type speaker. In a cabinet, a fixture attached to the back side of a speaker unit is extended and protruded outside the cabinet and attached to a wall face on which the cabinet is fixed. Since the speaker unit is attached to the wall face via the fixture, it is expected that the occurrence of vibration can be suppressed. JP-A-2001-78285 discloses the following prior art. A speaker unit is attached to an egg-shaped enclosure, and a rod-shaped member attached to the center of gravity of a magnetic circuit on the back of the speaker unit is extended to the back side. This rod-shaped member is mechanically supported and statically balanced by using a weight so as to suppress the occurrence of unnecessary vibration.
In the prior art disclosed in the Japanese Utility Model Registration No. 3008172 and JP-A-2001-78285, the speaker unit is also supported by the outside of the enclosure. Accordingly, a place where the speaker device can be installed is restricted. Further, it takes time and labor to install the speaker device. Even in the prior art disclosed in JP-UM-A-6-66194, since the speaker units are connected to each other by the binding member and also connected to the cabinet, it takes time and labor to attach the binding member.
In the speaker device, it is popular that the speaker unit is screwed to a front face of the speaker box or the cabinet. In this structure, vibration generated in the speaker unit tends to be transmitted to the enclosure. Therefore, sound, the phase of which is shifted, is generated from the surface of the enclosure. This deteriorates the reproduced sound. When the speaker unit is more strongly supported by mechanical means like the prior art described above, it can be expected that vibration generated by the speaker unit is suppressed. However, it takes more time and labor to more strongly support the speaker unit. Further, in order to mechanically support the speaker unit, the number of parts is increased. This raises the manufacturing cost.